On Tuesday, U.S. regulators accused the company of not reacting quick enough to fix defective gas pedals and threatened civil penalties, WSJ.com reports.

Secretary of Transportation Ray LaHood said in a statement, 'We're not finished with Toyota and are continuing to review possible defects and monitor the implementation of the recalls."

Another DOT official stated that the agency is considering a civil penalty against Toyota. If manufacturers don't issue a timely recall of defective vehicles, they can face a penalty of up to $16.4 million.

One analyst at Mizuno Credit Advisory said that if the new Prius model turns out to have a serious problem, it will have a "strong impact on Toyota's performance," as hybrid cars, are "almost the only cars selling well in Japan and the US."